Two-way, two-wire trunk for multi-office automatic exchange systems.



C. L. GOOURUM.

TWO-WAY, TWO-WIRE TRUNK ron MULTI-OFFICE AUTOMATIC IXCHANGE SYSTEMS.

APPL!CATION FILED DEC-5| I914- HENEWED MAR. 3 I911- 1,224,374.

Patented May 1, 1917.

lflvenfar C/mr/e s L. good/11m. y a

UNITED STATES PATENT OFFICE.

CHARLES L. GOODBUM, OF NEW YORK,, N. Y., ASSIGNOR, BY MESNE ASSIGNMENTS,TO WESTERN ELECTRIC COMPANY, INCORPORATED, A CO RPORATION OF'NEW YORK.

TWO-WAY, TWO-WIRE TRUNK FOR MUL'II-OFFICE AUT( MA'I'IC EXCHANGE SYSTEMS.

Application filed December 5, 1914, Serial No. 875,579.

provide a two-way trunk having an llllproved and con'iparatively simplearrangement of circuits and. apparatus. One ohject in ]')a-rtienlar isto provide a two-way trunk in which interference with the circuits byvarying ground potentials hetween otliees, is avoided.

In accordance with the invention, the trunk circuit is connected at hothcentral otfices through repeating coils to the multiple bank of anoutgoing selector, and also to the brushes ot-an incoming selector.(Jails at. one end of the trunlcenter at the bank ter minals of theoutgoing selector and are extended beyond the other end by the incominselector at that end] A relay at each endol the trunk controls theconnection of the trunk to either the bank terminals or the selectorbrushes at that end. The circuit established liet-wecu'the outgoingselector at one end of the trunk and the .incoming selector at the otherend. includes battery and ground at. one end only oi the trunk, wherebyinterference with the circuit byyvarying ground potentials between theofiiecs connected by the trunk is avoided.

The invention may he more readily understood by reference to theaccompanying drawing of a systemembodying the invention.

Referring to the drawings, the two-wire two-Way trunk tern'iinates atthe central oflice A in the [multiple bank of an outgoing selector 1 atlat the central ollice l in the brushes oi incoming selector 2. Forexample, a call from the subscribers station C for a called subscriberI), entering the office A, arrives at the bank terminals of theoutg'oing selector 1 and is extended heyontlthe other oflicc B theincoming se Specification of Letters Patent.

v Hatented May 1, 1917.

Renewed It arch 3 1917. Serial No. 152,434.

letter 2. li the opposite direction, calls over the. sani trunk arriveat the bank ternunals of an outgonig selector? at the ollice B, and are(Xl(llll(ll beyond the station by ineans oi the incoming selector Thus acall l'roni the subscribefis station [Q for a called subscr her l willenter the ollice l at the hank terninals ol' the outgoing selector 3 andwill ie extendcdlrv the incoming selector 4 at the olliee ll will heseen, therefore, that at each end of the trunk there is an outgoingandan incoming selector, and tl at the outgoingselector at one end cooperats with the incoming selector at the other end to extend a call.

At each e| d, the connection of the trunk to either the outgoing or theincoming selector is not er the control of a relay. the relay 5 atollice A, and the relay (1 rid. olliee B. Nor-mall" the trunkiseonuected at both ends to the ineoining selectors. at ollice A.through bacl; contacts 7 and h of relay '5 and repeating" coil 9 to thebrushes ol the selector-l, an I at ollice ll through hack contacts l0and l of relay-(5 and repeating coil 12 to the bru ihcs of the selector2.

The relay .i' is included in a third wire 13' local to the llice A, andthe relay (i is |il ewise includel in a third wire l-l local to the.ollice l3. call entering. l'or example. at the bank terminals ol theselector 1 results in the encrglzation,ol' the relay which thereupondirconnects that end of the trunk from the seltctor 4. and connects itthrough front contacts 15 and ll) of relay 5 and repeating coil 7 to theoutgoing selector I.

When a ca l is being, extended from either ollice over tlu trunk line, arelay at the other Ollie-e, relay l8 at ollice ll or relay .ll) at.ollice A, resp lads, and through circuit connections cont ollcd hy itover the third wire, renders the trunk 'busy at said other ()lllctL, Theoperat on of the system is as follows: Assume that the subscriber at C,whose line terminates a ollice A, desires to call the suhscribenat 1)whose line' terminates at olliec ll. Th: suhscribefls telephone line isextended in he usual manner through the line tinder 2|! and the brushesollhc outgoing seleeto- 1 to an idle trunk, the. two wires 21 and 22 ofwhich areconucctml to the contact t1 :ri'ninals of selector 1.Thereupon, a circlitis closed for the relay 5 as follows: from ground,through trunk relay 23, wire 13, relay 5, battery 24 to ground. Theresultant energization of relay 5, opens contacts 7 and 8 and closes contacts 15 and 16,'thereby disconnecting the two wires 25 and 26 of thetrunk from the selector '4 and connecting them to the outgoingselector 1. Though the trunk relay 23 is included in the circuit closedover the third wire 13, said relay does not operate, since it is amarginal relay and the windings of relay 5 are of such high resistancethat the. current flow in the circuit of the third wire is insufficientto operate the relay 23.

The subscribers line being extended from station 0 to selector 1, acircuit is estab lished for a relay 27, as follows: from batte .24,'rela27 wire 21, contact terminal an brush 0 selector 1, wire 28 of thetelephone line, the subscribers tele hone set,

, brush and contact terminal of selector 1, wire 22, to battery. Theresultant'operation of relay 27 closes contacts 30 and 31 of said relay.The closure ofcontact 31 controls the flow of current for the actuationof relay 23 for the. purpose of releasing the selector 1, as will behereinafter described.

The above mentioned closure of contact 30 establishes an operatingcircuit from oflice A to ofiice B over the trunk, as follows: frombattery 24 at oflice B, through contacts30 and 15, wire 25, contact 10,relay 18 contact 11, wire 26, contact 16 to battery. Thereupon relay18operates, closing its contacts 32- and 33. The closure of contact32-completes a circuit for a relay 34," which is thereu on actuated and,through. its contact 35,,p aces round upon the third wire 14, therebyr'e'n ering the trunk busy at oflice B. r v

The closure of contact 33 of relay 18 com- 'pletes the operating circuitfor the incomin selector 2 over the wires 36 and 37 whic are connectedto the brushes of said selector.

Circuits are thus established for extending the connection from theincomin selector 2 at office B to the called subscrfimers station D.That is, the calling subscriber at'station C, by operatin his dial,inter- .ru ts the above describ circuit through re ay 27. There is,therefore, a corresponding lnte'rruption of the circuit over the trunkwires 25 and 26 at contact 30 of relay 27. In turn, there is acorresponding interruption of the circuit of selector 2 at contact 33 ofrelay 18. The selector 2 andconnector 38 may thus be actuated in theusual manner from the dial at station C, to extend the connection to thecalled subscriber at station D. TlIQ'tWO wires 25, 26 of the trunk linebeing inductively connected through the repeating coil 17 at oflice Awith the callin line, and also being inductively 'connecte through therepeating coil contact 31 of relay 27 is to establish a releasingcircuit for selector 1 when the callin subscriber hangs up his receiver.This wi 1 now be described. The closure of contact 31, at the time thesubscriber at station 1C removes his receiver, completes a circuit for a.slow-actin relay 39. The resultant operation of sa-i relay closes itscontact 40, thereby completing a circuit for another slow-acting relay41, which thereupon closes its contact 42. Relays 39 and 41 bein of theslow-release type, do not respond to interruptions of the circuit atcontact 31 by the operation of the calling subscribers dial. However,when contact 31 is opened by the subscriber hangin up his receiver,relay 39 is released and c oses its ck contact 43. Relay'41 being of theslow-release type, maintains its contact 42'closed for an appreciabletime after contact 43 is closed, durin which interval operating currentis su plied to the marginal relay 23 over the f0 lowing circuit: fromgrounded battery,

.through contacts 43 and 42, wire 13, relay 23, to ground. Relay 23thereupon responds to close the circuit of release magnet 44 ofselector 1. It will be understood that the structure, operationandcircuit connections of the several switches at each end of the trunk maybe of an usual or known type and hence further i lustration anddescription thereof is deemed unnecessary.

What is claimed is:

1. In an automatic telephone exchange system, a two-wire trunk extendingbetween two central ofiices, an outgoin and an incoming selector forsaid truni at each of said oflice's, and automatically operated meansfor completing in either direction a battery connection to said trunk atone oflice and a connection free of batte to the incoming selector atthe other 0 cc.

2. In an automatic telephone exchange system, a trunk-extending betweentwo central olfices, selecting apparatus and a battery for said trunk ateach of said oflices, and

means operating automatically in'setting up a connection through saidtrunk in either direction for closing the trunk to battery at one end,and for maintaining it as a closed loop free from external connectionswith 1 battery. at the other end.

3. In an automatic telephone exchange As hereinbefore stated, thefunction of 70 ing end, and, for maintaining it as a clos loop freefif'om external connections with batter'y at the incoming end.

4. In an automatic telephone exchange system, a repeating trunkextending betwem two central offices, selecting apparatus and a batteryfor said trunk at each of said ofiices, said trunk being normallymaintained at each end as a closed loop tree from connections withbattery, means operating. automatically in setting upa connection tosaid trunk at either office for closing the trunk to battery at one endand for maintaining the normal condition thereof at the other end, andmeans for interrupting the trunk at the outgoing end to repeat callingimpulses to control the selecting apparatus at the incomin; end of thetrunk. Q

In an automatic telephone exchange system. a two-wire trunk between twocentral ofiices, an outgoing and an incoming selector for said trunk ateach of said oflices, a

local circuit at each oilice including multiple hank contacts of anoutgoing selector and battery, a second local circuit at each ofiice'including brushes of an incoming selector, two connecting circuits ateach oflice inductively connected, respectively, to said local circuits.and autrmlatically operated means at each ofiice for controlling theconnection of the trunk line to one or the other of said connecting ci:cuits at the respective offices.

6. In an automatic telephone exchange system, atw( Wire trunk betweentwo central offices, an outgoing and an incoming selector forsaic tru'nkat each of said oiiices, a local circuit at each office includingmultiple bank contacts of an'outgoing selector and necting circuits, andautomatically operated means at each office for disconnecting the trunkfrom tle incoming selector and trans fer-ring the c mnection, over theother connecting and local lector.

In witness whereof, I hereunto subscribe my name the 3rd day of DecemberA. D.,

CHARLES L. GOODRUM. Witnesses E. E01 ER,

.K. L. E ram.

circuits, to the outgoing'se-

